Gene therapy has rapidly emerged as an attractive strategy for the treatment of a wide variety of genetic disorders with particular focus on the respiratory and central nervous system (CNS).
Viruses have been extensively studied both pre-clinically and clinically and have demonstrated relatively efficient gene transfer, they exhibit certain limitations. Viral gene vectors, though relatively efficient, present a number of drawbacks including: low packaging capacity, technical difficulties in scale-up, high cost of production (Thomas, et al., Nat Rev Genet, 2003. 4(5): 346-58) and risk of mutagenesis (Olsen and Stein, N Engl J Med, 2004. 350(21): 2167-79). Furthermore, neutralizing immune responses may occur secondary to repeated administrations (Xiao, et al., J Virol, 1996. 70(11): 8098-108) or prior exposures (Chirmule, et al., J Virol, 2000. 74(5): 2420-5; Lowenstein, et al., Curr Gene Ther, 2007. 7(5): 347-60; Lowenstein, et al., Neurotherapeutics, 2007. 4(4): 715-24).
Non-viral gene vectors offer an attractive alternate strategy for gene delivery (O'Mahony, et al., J Pharm Sci, 2013. 102(10): 3469-84). Cationic polymer-based gene vectors provide a tailorable platform for DNA condensation and efficient gene transfer. Their positive charge density allows for stable compaction of negatively charged nucleic acids (Sun and Zhang, Mini Rev Med Chem, 2010. 10(2): 108-25; Dunlap, et al., Nucleic Acids Res, 1997. 25(15): 3095-101) and protects them from enzymatic degradation (Kukowska-Latallo, et al., Hum Gene Ther, 2000. 11(10): 1385-95). Also, the number of protonable amines provides increased buffering capacity that facilitates endosome escape via the “proton sponge effect”, leading to efficient transfection (Akinc, et al., J Gene Med, 2005. 7(5): 657-63; Akinc, and Langer, Biotechnol Bioeng, 2002. 78(5): 503-8). For these reasons cationic polymer based gene vectors exhibit successful gene delivery in vitro.
However, gene vectors offering high level transgene expression are usually associated with some level of cytotoxicity due to the highly cationic nature of these platforms. Moreover, in vivo delivery is hindered by their instability under physiological conditions (Mintzer and Simanek, Chem Rev, 2009. 109(2): 259-302) as well as their inability to penetrate biological barriers, such as the airway mucus (Suk, et al., J Control Release, 2014), the extracellular matrix and tumor tissues. Poly (β-amino ester) polymers (PBAE), in particular, provide a non-toxic, biodegradable polymer library for the compaction of DNA, offering highly effective gene delivery in vitro even in cells that are hard to transfect (Akinc, et al., Bioconjug Chem, 2003. 14(5): 979-88; Green, et al., Bioconjug Chem, 2006. 17(5): 1162-9; Zugates, et al., Bioconjug Chem, 2007. 18(6): 1887-96). Moreover, the subtle variations in the polymer backbone and end-capping groups offer cell type specific transgene expression (Tzeng, et al., Biomaterials, 2011. 32(23): 5402-10).
These vectors generally lack the means to overcome numerous extracellular biological barriers, resulting in low in vivo transgene delivery. The hydrolytic nature and relatively low positive charge density of these polymers results in drastically reduced colloidal stability and loose DNA compaction, thereby limiting their use in vivo and their potential for clinical applications. A delivery system for nucleic acid must provide efficient DNA compaction that will protect the DNA from serum nucleases and deliver the DNA to the target cells with effective high level transgene expression. Additionally, the formulation must be suitable for large scale production and stable in physiological conditions.
It is therefore an object of the present invention to provide biodegradable vectors having improved colloidal stability in physiological environments, enhanced penetration through biological barriers, tissue distribution, and delivery of nucleic acid payloads to the target cells.
It is a further object of the present invention to provide gene delivery vectors with low in vivo toxicity (i.e. acceptable safety profiles).